The present invention, in some embodiments thereof, relates to a method and system for watermarking a data sequence, and, more particularly, but not exclusively, to a method for watermarking data sequences of media content.
Recent developments in the field of digital audio and video have raised the problems of copyright protection and of monitoring the distribution of digital copies of audio and video content. Digital watermarking offers a solution to both copyright issues and to monitoring problems. Watermarking embeds a signature into the original data. The signature enables the owner to identify whether a given copy of the content is a legitimate copy. It is generally desired that the watermark be imperceptible to the user, particularly for audio and video content. The watermark should also be undetectable by non-owners in order to prevent duplication, and resistant enough to be reliably extracted from the copy even after the original data is transformed by operations such as transcoding, transducing, cropping, effects processing, equalization and so forth.
Data conversion techniques, such as multiple low bit-rate transcoding between different digital data formats and transducing, may have a strong impact on performance and robustness of existing watermarking schemes. A problem resulting from the sensitivity to data conversion is the difficulty of controlling audio recordings shared and transmitted via the Internet, or reproduced from radio channels, and other public media. For example, a broadcast signal, such as a song, may be recorded from the radio, transformed into digital form and distributed illegally. Ultimately, transcoded several times, transduced and transformed (with reverberation, echo, etc. applied), the watermark data may become unextractable.
While a number of audio watermarking schemes provide good robustness to transcoding based on psycho-acoustical models, audio signal transducing or effects processing remains a serious problem. Conversion of the audio data into an analog signal and the reproduction and subsequent conversion of the analog signal back to the digital form often destroys the watermarked data, making the watermark partially or completely unextractable.
U.S. Pat. Appl. 2001/0036292 by Levy et al. presents an autocorrelation-based watermarking technique, in which the based watermark is embedded by taking a copy of the image, lowering its level, and adding it slightly offset to the original image.
U.S. Pat. No. 6,999,598 by Foote et al. presents systems and methods for watermarking an original data by selectively dimensionally compressing or expanding a size of each of some or all of the portions along the given dimension, according to a given encoding scheme.